Patents of Otto Lilienthal

There are 25 known patents of Otto Lilienthal, most of them deal with
his work as a machanical engineer and owner of a factory for steam boilers
and engines, some concern with educational plays (invented together with his Brother Gustav), but only four have flying machines
as their subject:

The first German, English and American patents are similar and
cover gliders as well as a wing flapping machine. The second German patent
is an extension, the so-called "Vorflügel" (slat), a flap for automatic
attitude-changing in cases of negative angle of attack.